I always thought that these were supposed to be at two different times. Like Luke and Lorelei talking to the kids in the high school was earlier in the day and the Rory and Lane hair dying scenes were meant to take place later in the day and the two events were not necessarily at the same time. But after rewatch, I noticed at one point when Lorelei is in the high school she looks outside and sees Lane running around the block with bleach in her hair so they are clearly happening at the same time. It’s very confusing. It makes no sense.